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Heritability of Chick Viability for Two Breeds of the Domestic Fowl
MEASURING INTERIOR EGG QUALITY
Sharp, P. F., and C. K. Powell, 1930. Decrease in the internal quality of hen's eggs during storage as indicated by the yolk. Ind. Eng. Chem. 22: 909. Funk, E. M., 1948. The relation of the yolk index determined in natural position to the yolk index as determined after separating the yolk from the albumen. Poultry Sci. 27: 367. Baker, R. C, F. W. Hill, A. van Tienhoven and J. H. Bruckner, 1951. Effect of nicarbazin on egg quality. Poultry Sci. 36: 718-726.
481
Lorenz, F. W., 1953. Personal communication. Univ. of Calif., Davis, Calif. Hoist, W. F., and H. J. Almquist, 1931. Measurement of deterioration of stored hen's eggs. Hilgardia, 6: 49-60. Stadelman, W. J., J. V. Spencer, E. A. Sauter and M. V. Waanen, 1957. Egg preferences of Spokane consumers. Poultry Sci. 36: 596-601. Sharp, P. F., 1929. The pH of the whites as an important factor influencing the keeping quality of hen's eggs. Sci. 69: 278-280.
Heritability of Chick Viability for Two Breeds of the Domestic Fowl MORRIS
(Received for publication August 25, 1958)
INTRODUCTION
Poultry Research Centre it was decided to perform analyses on the three periods (i) HE few reports which are available from hatching up to three weeks of age suggest that heritability of chick via(warm brooder), (ii) from three to six bility is extremely low. Wilson (1948) estiweeks of age (cold brooder) and (iii) from mated heritability of viability to 8 weeks hatching to six weeks of age. The inclusion of age on an inbred flock of White Legof chickens in the analysis for the second horns as 11.8 percent and after correction period was conditional on their survival for for inbreding this figure was reduced to 5.2 the first period. percent. Hale (1954), using records of a Three flocks were chosen for the study, White Wyandotte flock collected for a period of six years, estimated heritability two of which were White Leghorn and the for the period up to 8 weeks as 7.4 percent third an Australorp flock. One of the White (betweens sires) and 14.3 percent (between Leghorn flocks, the Control, has been propdams). Brunson et al. (1956) have used the agated each year (since 1947) by random period from hatching date to 10 weeks of matings and the other, the M-flock has age to provide their average figure of 5 been selected on a combined family and inpercent based on two breeds and their dividual basis, initially for some character reciprocal crosses. More recently, Dickerson associated with egg production, but more (1957) obtained estimates of 2 percent and recently (1956 and 1957) selection has 13 percent respectively, from paternal half- been for a high production index. The Aussib and. full-sib correlations for the period tralorp flock has similarly been selected for from 0-10 weeks. All the above estimates a high production index. All chickens have been obtained from the matings of cockare in close agreement. erels and pullets. MATERIALS AND METHODS Observations recorded for five successive As considerable information on chick years, commencing in 1953, have been used mortality to all ages was available at the in this study. A varying number of hatches
T
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 28, 2015
J. A.
C.S.I.R.O. Division of Animal Health and Production, Poultry Research Centre, Werribee, Victoria, Australia
482
J. A. MORRIS
TABLE 1 .—Mortality
Flock
M Leghorn
Total Control Leghorn
Total Combined Leghorn Total Australorp
Total Australorp
Year
for a given hatch. This was an unfortunate necessity resulting from management difficulties associated with the pedigree hatching and wing banding of 2,000 to 3,000 chicks on one day. The different breeds were not allowed to intermix until after six weeks of age when they were moved to free range. No attempt has been made to eliminate accidental deaths from the results and the figures presented represent those from unculled flocks (with the exception of the elimination of males in all cases other than for the 1957 hatched Australorps). RESULTS AND DISCUSSION A total of 8,379 chickens was used in the present study which included progeny from 151 sires and 1,340 dams. Details of the distribution of these chicks together with the mortality recorded during brooding are given in Table 1. Most of the deaths occurred in the early stages of rearing but it is not possible to supply details concerning
of chickens for three flocks during brooding periods
Sires
Dams
No. of chicks
Warm brooder (0-3 weeks)
Total brooder (1-6 weeks)
Dead
%
Dead
%
1953 1954 1955 1956 1957
15 13 14 12 10
114 127 153 102 123
845 973 1,054 307 800
112 108 90 42 36
13.3 11.1 8.5 13.7 4.5
121 139 139 62 86
14.3 14.3 13.2 20.2 10.8
5
64
619
3,979
388
9.8
547
13.7
1953 1954 1955 1956 1957
8 8 8 8 12
65 61 83 45 95
346 277 431 199 461
39 39 43 56 17
11.3 14.1 10.0 28.1 3.7
42 51 57 56 31
12.1 18.4 13.2 28.1 6.7
44
349
1,714
194
11.3
237
13.8
5
108
968
5,693
582
10.2
784 '
13.8
1953 1954 1955 1956 1957
11 10 11 5 6
83 85 91 44 69
548 498 613 129 898
106 146 132 42 166
19.3 29.3 21.5 32.6 18.5
112 164 145 44 211
20.4 32.9 23.7 34.1 23.5
5
43
372
2,686
592 •
22.0
676
25.2
5
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 28, 2015
was required to obtain replacements over the period concerned, the largest number being in 1953 when 8 weekly hatches were taken off. This number was effectively reduced and in 19S6 and 1957 only 3 fortnightly spaced hatches were required. The experimental material refers to pullet chickens only, with the one exception that in 1957 both pullet and cockerel chickens of the Australorp breed were included in the sample. General details of brooding, management, etc. have been supplied by Skaller (1957). In brief, however, the chickens were kept in electrically heated battery brooders (warm brooders) for the first three weeks and then transferred to cold brooders where they remained up to six weeks of age. Within breeds and within sires all chicks were randomly allotted to the different brooder units with the one exception that in nearly all cases the progeny of a single dam, were placed in the same brooder unit
483
HERITABILITY or CHICK VIABILITY TABLE 2.-—Heritability
estimates pooled within years Breed
White Leghorn
Method of estimation
Australorp M-flock
C-flock
M & C (pooled)
(i) 0-3 weeks (Warm Brooder) (i) 0.042 0.216
(ii) 0.033 0.092
0.025 0.361
(ii) 0.014 0.048
(i) 0.022 0.374
(ii) 0.021 0.068
(b)
0.049
0.020
0.033
0.028
0.046
0.016
0.060
0.027
0.032
0.018
0.037
0.030
0.035
0.015
0.039
0.023
(ii)
Sire
Weighted Average of Sire Estimates*
(ii) 3-6 weeks {Cold Brooder)
•
W \Dam
(i) 0.022 0.180
(ii) 0.018 0.056
(i) 0.013 0.204
(ii) 0.030 0.096
(i) 0.020 0.179
(ii) 0.015 0.044
(i) 0.000 0.073
(b)
0.027
0.017
0.046
0.034
0.032
0.015
0.000
0.025
0.017
0.028
0.032
0.026
0.015
0.000
, N. /Sire Sire
Weighted Average of Sire Estimates*
0.068
(iii) 0-6 -weeks {Total Brooder) fal / S i r e w \Dam
(i) 0.028 0.312
(ii) 0.018 0.052
0.055 0.201
(0
(ii) 0.037 0.088
(i) 0.034 0.280
(ii) 0.016 0.044
(i) 0.014 0.364
(ii) 0.019 0.068
(b)
0.053
0.020
0.048
0.032
0.053
0.017
0.053
0.026
0.040
0.019
0.052
0.034
0.043
0.016
0.030
0.022
Sire
Weighted Average of Sire Estimates*
* The sire estimates obtained from both methods of estimation have been given weight according to the inverse of their standard errors and a weighted average obtained. Columns headed by (i) contain estimates of heritability. Columns headed by (ii) contain standard errors of estimates of heritability.
cause of death as autopsies were not generally performed on chickens. It was apparent, nevertheless, that specific diseases were not important in causing the death of chicks during the first three weeks. During the second three weeks coccidiosis was the principal infectious disease. The severity of infection varied from year to year and was of negligible importance in 1956 and 1957. Heritability has been estimated using the methods described by Lush et al. (1948) and Robertson and Lerner (1949); hereafter, these will be referred to as methods
(a) and (b) respectively. Using method (a) estimates were obtained from the sire and dam components of variance whereas using method (b) estimates were obtained only between sires. The results of both analyses, for the two periods and for the total, are given in Table 2. These results are pooled within years. As there were no significant differences between the two Leghorn flocks both analyses were pooled to yield a within strain estimate for this breed. In addition, since the estimates obtained from the analysis between sires provide a more realistic pic-
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 28, 2015
(ii) 0.016 0.056
C)
« {cTm
(i) 0.019 0.416
484
J. A. MORRIS
ture of the true genetic situation than do those obtained between dams, the estimates from the analysis between sires for the two methods were combined for each of the three periods. Heritability is extremely low for all periods, and there is little variation between the two breeds. For the period from 0-3 weeks heritability is 3.5 percent for the Leghorns and 3.9 percent for the Australorps, the standard errors being respectively l.S and 2.3 percent. Similarly for the first six weeks of brooding the values are 4.3 percent for Leghorns and 3.0 per-
cent for Australorps with standard errors of 1.6 and 2.2 percent, respectively. Despite the large number of degrees of freedom associated with all estimates the size of the error is always large. Statistical significance is attained in most cases even though the actual estimate does not exceed twice its standard error. It should be remembered that in dealing with correlation coefficients (and likewise heritabilities) that the distribution is extremely skew for low values of the correlation and, in reality, these errors do not have a great deal of
Breed White Leghorn Year
M-flock
Australorp C-flock Sire*
Damf
0.08 0.00 0.08 0.00 0.02
0.43 0.46 0.31 0.48 0.22 0.37
0.09
0.02
0.07
0.00 0.04 0.08 0.00 0.00 0.01
0.20 0.25 0.02 0.00 0.40 0.20
0.00 0.04 0.00 0.00 0.00 0.00
0.07 0.00 0.26 0.00 0.26 0.07
0.06
0.03
0.10
0.00 0.03 0.09 0.00 0.00 0.03
0.39 0.32 0.30 0.12 0.26 0.31
0.03 0.24 0.00 0.16 0.00 0.06
0.32 0.13 0.32 0.09 0.36 0.20
0.06 0.00 0.08 0.00 0.00 0.01
0.34 0.40 0.33 0.46 0.31 0.36
0.02
0.05
0.04
0.09
0.02
0.07
Damf
Sire*
Damf
0.00 0.04 0.00 0.04 0.01 0.02
0.38 0.40 0.51 0.06 0.30 0.42
0.01 0.10 0.00 0.13 0.00 0.04
0.44 0.22 0.35 0.00 0.28 0.22
0.02
0.06
0.03
0.00 0.00 0.05 0.01 0.03 0.02
0.00 0.10 0.31 0.00 0.17 0.18
0.02
Sire* (7) 0-3 weeks (Warm Brooder) 1953 1954 1955 1956 1957 Pooled Within Years Standard Error of Pooled Estimate
o:oo
(ii) 3-6 weeks (Cold Brooder) 1953 1954 1955 1956 1957 Pooled Within Years Standard Error of Pooled Estimate
0.07
(iii) 0-6 weeks (Total Brooder) 1953 1954 1955 1956 1957 Pooled Within Years Standard Error of Pooled Estimate
* Estimated from Sire Component of Variance, f Estimated from Dam Component of Variance.
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TABLE 3.—Yearly estimates of heritability using method (a)
HERITABILITY OF CHICK VIABILITY
tent in later periods. This should apply particularly to general health and vitality. The reduced contributions by dams to variance for the second period could reflect a reduced maternal influence but at the same time the effect of common environment might be less marked in cold brooders than in warm brooders. SUMMARY
Heritability of chick viability has been estimated as 3.5 percent for White Leghorn and 3.9 percent for 'Australorp for the period 0-3 weeks and 4.3 percent for White Leghorn and 3.0 percent for Australorp for the first six weeks of life. The respective standard errors for these estimates were 1.5, 2.3, 1.6 and 2.2 percent. Two different methods of estimation have been used to obtain these estimates and the individual values show fair agreement. The large contribution to variance between dams is suggestive of important maternal effects for the period 0-3 weeks but the limitations of the data only permit general conclusions. REFERENCES Brunson, C. C, G. F. Godfrey and B. L. Goodman, 1956. Heritability of all-or-none traits: hatchability and resistance to death to ten weeks of age. Poultry Sci. 35: 516-523. Dickerson, G. E., 1957. Genetic variation in some economic characters of Leghorn-type chickens. Poultry Sci. 36: 1113. Hale, R. H., 1954. Heritability of chick viability in a White Wyandotte flock. J. Agric. Sci. 44: 221-226. Lush, J. L., W. F. Lamoreux and L. N. Hazel, 1948. The heritability of resistance to death in the fowl. Poultry Sci. 27: 375-388. Robertson, A., and I. M. Lerner, 1949. The heritability of all-or-none traits: viability in poultry. Genetics, 34: 395-411. Skaller, F., 1957. C.S.I.R.O. Poultry Research Centre, Werribee, Victoria. Division of Animal Health and Production. Technical Paper No. 2 (superseding No. 1). Wilson, W. O., 1948. Viability of embryos and of chicks in inbred chickens. Poultry Sci. 27: 727735,
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value. Hale reported errors of considerably lesser magnitude but it would appear that these are errors of the intra-class correlations and not of the heritabilities. The previously mentioned reports of Hale (1954) and Brunson et al. (1956) disclose evidence for the presence of maternal effects. The magnitude of the maternal influence is generally gauged by the extent to which the component of variance "between dams within sires" is in excess of the analogous component "between sires." All this difference, if it exists, cannot be attributed to maternal influence only, as dominance, epistasis and environmental effects common to the progeny of a dam help to inflate the "between dams within sires" component of variance. In our data it is impossible to separate these effects and since there was a tendency for the progeny of each dam to be placed in the same brooder unit for a given hatch, the environmental component could be a further factor in inflating this component. However, since the mortality results for each dam were based on the totality of observations for the whole hatching period, this factor should be of negligible magnitude. It will be seen from Table 3 that, for the period 0-3 weeks, heritability estimated from the dam component, is in excess of the estimate obtained from the sire component in nearly all cases. In addition, the differences are quite large. Unfortunately little more than this can be said. There is some evidence for a maternal influence but this is not conclusive. The results for the period 3-6 weeks do add supporting evidence, however, for the M Leghorn and for the Australorp flock. In both these groups the contribution to variance "between dams within sires" is relatively much smaller than it is for the first three weeks period. It does not seem unreasonable to expect maternal effects to be more marked during the earlier post hatching period and less persis-
485
Sharp, P. F., and C. K. Powell, 1930. Decrease in the internal quality of hen's eggs during storage as indicated by the yolk. Ind. Eng. Chem. 22: 909. Funk, E. M., 1948. The relation of the yolk index determined in natural position to the yolk index as determined after separating the yolk from the albumen. Poultry Sci. 27: 367. Baker, R. C, F. W. Hill, A. van Tienhoven and J. H. Bruckner, 1951. Effect of nicarbazin on egg quality. Poultry Sci. 36: 718-726.
481
Lorenz, F. W., 1953. Personal communication. Univ. of Calif., Davis, Calif. Hoist, W. F., and H. J. Almquist, 1931. Measurement of deterioration of stored hen's eggs. Hilgardia, 6: 49-60. Stadelman, W. J., J. V. Spencer, E. A. Sauter and M. V. Waanen, 1957. Egg preferences of Spokane consumers. Poultry Sci. 36: 596-601. Sharp, P. F., 1929. The pH of the whites as an important factor influencing the keeping quality of hen's eggs. Sci. 69: 278-280.
Heritability of Chick Viability for Two Breeds of the Domestic Fowl MORRIS
(Received for publication August 25, 1958)
INTRODUCTION
Poultry Research Centre it was decided to perform analyses on the three periods (i) HE few reports which are available from hatching up to three weeks of age suggest that heritability of chick via(warm brooder), (ii) from three to six bility is extremely low. Wilson (1948) estiweeks of age (cold brooder) and (iii) from mated heritability of viability to 8 weeks hatching to six weeks of age. The inclusion of age on an inbred flock of White Legof chickens in the analysis for the second horns as 11.8 percent and after correction period was conditional on their survival for for inbreding this figure was reduced to 5.2 the first period. percent. Hale (1954), using records of a Three flocks were chosen for the study, White Wyandotte flock collected for a period of six years, estimated heritability two of which were White Leghorn and the for the period up to 8 weeks as 7.4 percent third an Australorp flock. One of the White (betweens sires) and 14.3 percent (between Leghorn flocks, the Control, has been propdams). Brunson et al. (1956) have used the agated each year (since 1947) by random period from hatching date to 10 weeks of matings and the other, the M-flock has age to provide their average figure of 5 been selected on a combined family and inpercent based on two breeds and their dividual basis, initially for some character reciprocal crosses. More recently, Dickerson associated with egg production, but more (1957) obtained estimates of 2 percent and recently (1956 and 1957) selection has 13 percent respectively, from paternal half- been for a high production index. The Aussib and. full-sib correlations for the period tralorp flock has similarly been selected for from 0-10 weeks. All the above estimates a high production index. All chickens have been obtained from the matings of cockare in close agreement. erels and pullets. MATERIALS AND METHODS Observations recorded for five successive As considerable information on chick years, commencing in 1953, have been used mortality to all ages was available at the in this study. A varying number of hatches
T
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 28, 2015
J. A.
C.S.I.R.O. Division of Animal Health and Production, Poultry Research Centre, Werribee, Victoria, Australia
482
J. A. MORRIS
TABLE 1 .—Mortality
Flock
M Leghorn
Total Control Leghorn
Total Combined Leghorn Total Australorp
Total Australorp
Year
for a given hatch. This was an unfortunate necessity resulting from management difficulties associated with the pedigree hatching and wing banding of 2,000 to 3,000 chicks on one day. The different breeds were not allowed to intermix until after six weeks of age when they were moved to free range. No attempt has been made to eliminate accidental deaths from the results and the figures presented represent those from unculled flocks (with the exception of the elimination of males in all cases other than for the 1957 hatched Australorps). RESULTS AND DISCUSSION A total of 8,379 chickens was used in the present study which included progeny from 151 sires and 1,340 dams. Details of the distribution of these chicks together with the mortality recorded during brooding are given in Table 1. Most of the deaths occurred in the early stages of rearing but it is not possible to supply details concerning
of chickens for three flocks during brooding periods
Sires
Dams
No. of chicks
Warm brooder (0-3 weeks)
Total brooder (1-6 weeks)
Dead
%
Dead
%
1953 1954 1955 1956 1957
15 13 14 12 10
114 127 153 102 123
845 973 1,054 307 800
112 108 90 42 36
13.3 11.1 8.5 13.7 4.5
121 139 139 62 86
14.3 14.3 13.2 20.2 10.8
5
64
619
3,979
388
9.8
547
13.7
1953 1954 1955 1956 1957
8 8 8 8 12
65 61 83 45 95
346 277 431 199 461
39 39 43 56 17
11.3 14.1 10.0 28.1 3.7
42 51 57 56 31
12.1 18.4 13.2 28.1 6.7
44
349
1,714
194
11.3
237
13.8
5
108
968
5,693
582
10.2
784 '
13.8
1953 1954 1955 1956 1957
11 10 11 5 6
83 85 91 44 69
548 498 613 129 898
106 146 132 42 166
19.3 29.3 21.5 32.6 18.5
112 164 145 44 211
20.4 32.9 23.7 34.1 23.5
5
43
372
2,686
592 •
22.0
676
25.2
5
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 28, 2015
was required to obtain replacements over the period concerned, the largest number being in 1953 when 8 weekly hatches were taken off. This number was effectively reduced and in 19S6 and 1957 only 3 fortnightly spaced hatches were required. The experimental material refers to pullet chickens only, with the one exception that in 1957 both pullet and cockerel chickens of the Australorp breed were included in the sample. General details of brooding, management, etc. have been supplied by Skaller (1957). In brief, however, the chickens were kept in electrically heated battery brooders (warm brooders) for the first three weeks and then transferred to cold brooders where they remained up to six weeks of age. Within breeds and within sires all chicks were randomly allotted to the different brooder units with the one exception that in nearly all cases the progeny of a single dam, were placed in the same brooder unit
483
HERITABILITY or CHICK VIABILITY TABLE 2.-—Heritability
estimates pooled within years Breed
White Leghorn
Method of estimation
Australorp M-flock
C-flock
M & C (pooled)
(i) 0-3 weeks (Warm Brooder) (i) 0.042 0.216
(ii) 0.033 0.092
0.025 0.361
(ii) 0.014 0.048
(i) 0.022 0.374
(ii) 0.021 0.068
(b)
0.049
0.020
0.033
0.028
0.046
0.016
0.060
0.027
0.032
0.018
0.037
0.030
0.035
0.015
0.039
0.023
(ii)
Sire
Weighted Average of Sire Estimates*
(ii) 3-6 weeks {Cold Brooder)
•
W \Dam
(i) 0.022 0.180
(ii) 0.018 0.056
(i) 0.013 0.204
(ii) 0.030 0.096
(i) 0.020 0.179
(ii) 0.015 0.044
(i) 0.000 0.073
(b)
0.027
0.017
0.046
0.034
0.032
0.015
0.000
0.025
0.017
0.028
0.032
0.026
0.015
0.000
, N. /Sire Sire
Weighted Average of Sire Estimates*
0.068
(iii) 0-6 -weeks {Total Brooder) fal / S i r e w \Dam
(i) 0.028 0.312
(ii) 0.018 0.052
0.055 0.201
(0
(ii) 0.037 0.088
(i) 0.034 0.280
(ii) 0.016 0.044
(i) 0.014 0.364
(ii) 0.019 0.068
(b)
0.053
0.020
0.048
0.032
0.053
0.017
0.053
0.026
0.040
0.019
0.052
0.034
0.043
0.016
0.030
0.022
Sire
Weighted Average of Sire Estimates*
* The sire estimates obtained from both methods of estimation have been given weight according to the inverse of their standard errors and a weighted average obtained. Columns headed by (i) contain estimates of heritability. Columns headed by (ii) contain standard errors of estimates of heritability.
cause of death as autopsies were not generally performed on chickens. It was apparent, nevertheless, that specific diseases were not important in causing the death of chicks during the first three weeks. During the second three weeks coccidiosis was the principal infectious disease. The severity of infection varied from year to year and was of negligible importance in 1956 and 1957. Heritability has been estimated using the methods described by Lush et al. (1948) and Robertson and Lerner (1949); hereafter, these will be referred to as methods
(a) and (b) respectively. Using method (a) estimates were obtained from the sire and dam components of variance whereas using method (b) estimates were obtained only between sires. The results of both analyses, for the two periods and for the total, are given in Table 2. These results are pooled within years. As there were no significant differences between the two Leghorn flocks both analyses were pooled to yield a within strain estimate for this breed. In addition, since the estimates obtained from the analysis between sires provide a more realistic pic-
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 28, 2015
(ii) 0.016 0.056
C)
« {cTm
(i) 0.019 0.416
484
J. A. MORRIS
ture of the true genetic situation than do those obtained between dams, the estimates from the analysis between sires for the two methods were combined for each of the three periods. Heritability is extremely low for all periods, and there is little variation between the two breeds. For the period from 0-3 weeks heritability is 3.5 percent for the Leghorns and 3.9 percent for the Australorps, the standard errors being respectively l.S and 2.3 percent. Similarly for the first six weeks of brooding the values are 4.3 percent for Leghorns and 3.0 per-
cent for Australorps with standard errors of 1.6 and 2.2 percent, respectively. Despite the large number of degrees of freedom associated with all estimates the size of the error is always large. Statistical significance is attained in most cases even though the actual estimate does not exceed twice its standard error. It should be remembered that in dealing with correlation coefficients (and likewise heritabilities) that the distribution is extremely skew for low values of the correlation and, in reality, these errors do not have a great deal of
Breed White Leghorn Year
M-flock
Australorp C-flock Sire*
Damf
0.08 0.00 0.08 0.00 0.02
0.43 0.46 0.31 0.48 0.22 0.37
0.09
0.02
0.07
0.00 0.04 0.08 0.00 0.00 0.01
0.20 0.25 0.02 0.00 0.40 0.20
0.00 0.04 0.00 0.00 0.00 0.00
0.07 0.00 0.26 0.00 0.26 0.07
0.06
0.03
0.10
0.00 0.03 0.09 0.00 0.00 0.03
0.39 0.32 0.30 0.12 0.26 0.31
0.03 0.24 0.00 0.16 0.00 0.06
0.32 0.13 0.32 0.09 0.36 0.20
0.06 0.00 0.08 0.00 0.00 0.01
0.34 0.40 0.33 0.46 0.31 0.36
0.02
0.05
0.04
0.09
0.02
0.07
Damf
Sire*
Damf
0.00 0.04 0.00 0.04 0.01 0.02
0.38 0.40 0.51 0.06 0.30 0.42
0.01 0.10 0.00 0.13 0.00 0.04
0.44 0.22 0.35 0.00 0.28 0.22
0.02
0.06
0.03
0.00 0.00 0.05 0.01 0.03 0.02
0.00 0.10 0.31 0.00 0.17 0.18
0.02
Sire* (7) 0-3 weeks (Warm Brooder) 1953 1954 1955 1956 1957 Pooled Within Years Standard Error of Pooled Estimate
o:oo
(ii) 3-6 weeks (Cold Brooder) 1953 1954 1955 1956 1957 Pooled Within Years Standard Error of Pooled Estimate
0.07
(iii) 0-6 weeks (Total Brooder) 1953 1954 1955 1956 1957 Pooled Within Years Standard Error of Pooled Estimate
* Estimated from Sire Component of Variance, f Estimated from Dam Component of Variance.
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TABLE 3.—Yearly estimates of heritability using method (a)
HERITABILITY OF CHICK VIABILITY
tent in later periods. This should apply particularly to general health and vitality. The reduced contributions by dams to variance for the second period could reflect a reduced maternal influence but at the same time the effect of common environment might be less marked in cold brooders than in warm brooders. SUMMARY
Heritability of chick viability has been estimated as 3.5 percent for White Leghorn and 3.9 percent for 'Australorp for the period 0-3 weeks and 4.3 percent for White Leghorn and 3.0 percent for Australorp for the first six weeks of life. The respective standard errors for these estimates were 1.5, 2.3, 1.6 and 2.2 percent. Two different methods of estimation have been used to obtain these estimates and the individual values show fair agreement. The large contribution to variance between dams is suggestive of important maternal effects for the period 0-3 weeks but the limitations of the data only permit general conclusions. REFERENCES Brunson, C. C, G. F. Godfrey and B. L. Goodman, 1956. Heritability of all-or-none traits: hatchability and resistance to death to ten weeks of age. Poultry Sci. 35: 516-523. Dickerson, G. E., 1957. Genetic variation in some economic characters of Leghorn-type chickens. Poultry Sci. 36: 1113. Hale, R. H., 1954. Heritability of chick viability in a White Wyandotte flock. J. Agric. Sci. 44: 221-226. Lush, J. L., W. F. Lamoreux and L. N. Hazel, 1948. The heritability of resistance to death in the fowl. Poultry Sci. 27: 375-388. Robertson, A., and I. M. Lerner, 1949. The heritability of all-or-none traits: viability in poultry. Genetics, 34: 395-411. Skaller, F., 1957. C.S.I.R.O. Poultry Research Centre, Werribee, Victoria. Division of Animal Health and Production. Technical Paper No. 2 (superseding No. 1). Wilson, W. O., 1948. Viability of embryos and of chicks in inbred chickens. Poultry Sci. 27: 727735,
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value. Hale reported errors of considerably lesser magnitude but it would appear that these are errors of the intra-class correlations and not of the heritabilities. The previously mentioned reports of Hale (1954) and Brunson et al. (1956) disclose evidence for the presence of maternal effects. The magnitude of the maternal influence is generally gauged by the extent to which the component of variance "between dams within sires" is in excess of the analogous component "between sires." All this difference, if it exists, cannot be attributed to maternal influence only, as dominance, epistasis and environmental effects common to the progeny of a dam help to inflate the "between dams within sires" component of variance. In our data it is impossible to separate these effects and since there was a tendency for the progeny of each dam to be placed in the same brooder unit for a given hatch, the environmental component could be a further factor in inflating this component. However, since the mortality results for each dam were based on the totality of observations for the whole hatching period, this factor should be of negligible magnitude. It will be seen from Table 3 that, for the period 0-3 weeks, heritability estimated from the dam component, is in excess of the estimate obtained from the sire component in nearly all cases. In addition, the differences are quite large. Unfortunately little more than this can be said. There is some evidence for a maternal influence but this is not conclusive. The results for the period 3-6 weeks do add supporting evidence, however, for the M Leghorn and for the Australorp flock. In both these groups the contribution to variance "between dams within sires" is relatively much smaller than it is for the first three weeks period. It does not seem unreasonable to expect maternal effects to be more marked during the earlier post hatching period and less persis-
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